Laser welding is currently used to carry out robotic welding. Japanese Laid-Open Patent Publication No. 2005-177862 discloses an example of such a welding technique. A laser irradiating device is installed at a tip of a robotic arm for irradiating a laser beam. The robotic arm is moved and changes an irradiating direction of the laser beam emitted from the laser irradiating device such that a predetermined welding point is welded by moving the laser beam. Such type of welding is referred to as remote welding, which is often used when a distance between a work piece and the laser irradiating device is farther than that of the conventional welding.
When the robotic arm is implemented as described above, it may be necessary to adjust the focus of the laser beam according to the distance from the laser irradiating device to the laser irradiating point on the work piece. Japanese Laid-Open Patent Publication No. (Hei.) 5-2146 discloses a method for adjusting the laser focusing distance. Such a method comprises measuring the distance from the laser irradiating device to the laser irradiating point on the work piece and adjusting a lens system within the laser irradiating device.